Mixing or dissolving apparatus, etc



May 23, 1939.

G. M LEAN 2,159,856

MIXING OR DISSOLVLNG APPARATUS, ETC

Filed July 31, 1937 INVENTOR.

M ATTORNEYS Patented May 23, 1939 PATENT OFFICE 2,159,856 MIXING BDISSOLVING APPARATUS, ETC

Gordon Macbean,

Flushing, N. Y., minor to The Turbo-Mixer Corporation, New York, N. Y.,a corporation of New York Application July 31, 1937, Serial No. 156,864

2 Claim.

This invention relates to mixing apparatus and to dissolving apparatus.It is particularly applicable to mixing or dissolving tanks in whichliquid is repeatedly recirculated by one or more rotating impellers,each of which discharges the liquid outwardly in tangential orquasi-tangential directions.

When such a rotating impeller acts on liquid of low viscosity in a plaincylindrical tank, the

i0 rotary motion of the impeller is imparted to the mass oi liquid. Theliquid swirls and a vortex forms over the impeller. Thus, the mixingaction is poor, since the whole mass of liquid tends to move as a unit,with the elemental volumes l5 travelling in nearly circular paths.

With a very viscous liquid the drag of the tank wall on the liquidlargely counteracts the tendency of the entire mass to swirl. The vortexis relatively small. The elemental volumes of the 20 liquid are drawninwardly by the impeller, in pronounced spiral paths, and the mixingaction is satisfactory. To obtain similar mixing action with a liquid01' low viscosity, it is usual to place bailles on the tank wall for thepurpose of estab- 25 lishing the necessary drag between the tank andlthe mass of liquid. As the viscosity of the liquid increases, thebailllng required decreases until a point is reached beyond whichbaflling is detrimental to the mixing action. With very high 30viscosity material, the battles have the effect of forming pocketsadjacent to the tank wall. Such parts of the mix as are in thesepockets, tend to stay there and are not effectively recirculated andintermixed with the rest of the material in 3 the tank. Additionally,the power required to rotate the impeller under such conditions isundesirably large.

From the foregoing, it will be seen that satisfactory mixing with theprior art apparatus, re-

quires different installations for materials of high and low viscosity.Often this necessitates extra installations .which cannot be used tocapacity. But an even more serious drawback exists in processes thatcause the material to undergo a 45 great change in viscosity during themixing or dissolving treatment. Some examples of such processes arepaint pigmentation, the manufacture of clay slurries and asphaltemulsions, and the dissolving of materials used in making rayon,

50 acetate silk, and lacquers, e. g., dissolving xanthate materials in asolution of caustic soda. For such processes, the prior art mixingapparatus can be no more than a compromise which will functionefflciently only at an intervening 55 viscosity. The time and the energyrequired to carry out the process are increased accordingly.

A general object of the present invention is to provide mixing ordissolving apparatus which functions efiiciently with material of eitherhigh or low viscosity. 5

Another object of the invention is to provide mixing or dissolvingapparatus which functions efficiently as the mix progressively increasesin viscosity.

More specific objects of the invention are to equip mixing or dissolvingapparatus with bodies which have diminishing effect as the viscosity ofthe mix increases, and to provide a suitable method of determining thebest placement of such bafiles.

Other specific objects are to provide a baille which has full effect atlow viscosity and virtually no eiiect at high viscosity, and to providea method of placement for such a baflle.

Various additional objects and advantages will be apparent to thoseskilled in the art from a consideration of the following disclosure.

In general, the circulation in the tank is along paths outwardly of theimpeller toward the side of the tank, along the tank wall in a helicalpath, inwardly of the tank wall toward the axis of the impeller, andlengthwise of such axis back to the impeller ior recirculation. This isa complex path of movement involving vertical and horizontal componentsof motion. For convenience and clarity the path of flow will bediscussed hereinafter in terms of the vertical and horizpntal componentsoi motion.

Two suitable forms of construction are shown. by way of example, in theaccompanying drawmg, wherein:

Fig. l is a largely diagrammatic vertical section through a two-impellermixer embodying the present invention, the view being takenapproximately on line I-l of Fig. 2; Fig. 2 is a largely diagrammaticplan view of the same; Fig. 3 is a diagram indicating the horizontalcomponent of the flow in the case of a liquid 01 low viscosity;

Fig. 4 is a diagram indicating the horizontal component of, the flow inthe case of a liquid of high viscosity; and

Fig. 5 is a largely diagrammatic vertical section through asingle-impeller mixer.

In Figs. 1 and 2 a tank designated as a whole by 5 has a cylindricalside wall I, and has a top flange 8 to receive a cover (not shown).Depending coaxially into the tank is a vertical shalt 9 that is rotatedby any suitable source 0! power I (not shown). Mounted on the shaft arespaced involute impellers Ill and II which may be of convenional formbut which are preferably of the "tilted variety disclosed in UnitedStates Patent 1,908,002. In a zone above impeller Ill there is affixedto tank wall I a series of baffles I2 (four shown). In the zone betweenimpellers III and II there is afiixed to tank wall I a second series ofbaiiles I3 (four shown).

The bailles I2 and [3 may be mounted with the aid of any suitable means.the drawing merely showing supporting rods II to illustrate the mountingin a diagrammatic manner. Each of the baiiies I2 and i3 extends in agenerally vertical direction and is spaced inwardly from the tank wallI, as shown in the drawing. Additionally, each of the baflles I2 and I3is positioned at an angle to the tank radius, with its trailinglongitudinal edge if farther from the tank wall than its leading edge 1.Each of bailies I2 is also inclined from bottom to top circumferentiallyof the tank in the direction of impeller rotation. Baiiies I3 arepositioned vertically.

The action of the baiiles in opposing swirling of the liquid isillustrated in Fig. 3. The spiral line I indicates the horizontalcomponent of the path which an elemental volume of relatively lowviscosity liquid would follow in the absence of baflles. With thebaffles present, the liquid moving in the same direction at Ill strikesa bailie (I! or l3) and is projected at H toward the axial zone of thetank.

As the viscosity of the mix increases, the path l5 becomes a more andmore pronounced spiral, with the result that the bailles present lessand less effective surface to the spiral flow. Thus the effect of thebailies decreases as the viscosity increases. With very high viscositythe horizontal component of flow without baffles wouldbe as indicated byline I5 in Fig. 4. It will be apparent that this path is such that thebaffles I2 and I3 are positioned edgewise to the flow and hence offeronly skin friction resistance.

With regard to the vertical component of flow, the tank may beconsidered as divided into superimposed flow zones. roughly indicated inFig. 1 by dotted flow lines. Each of the impellers is in a zone ofoutward flow. Adjacent each side of each zone of outward flow is a zoneof flow axially of the tank. And the zones of axial flow merge intozones of inward flow.

This vertical component of flow is very effective in promoting themixing or dissolving, and hence it should be impeded as little aspossible. As an elemental volume of liquid moves upwardly (e. g., alongcircuit d) it also moves circumferentially of the tank in the directionof impeller rotation (see Fig. 3). Thus, the resultant path is on anincline, upwardly and circumferentially in the direction of impellerrotation. As the longitudinal axes of baflies I2 are alsocorrespondingly inclined these bailles oiier only skin frictionresistance to the vertical component of flow.

As the flow in circuit b baflles I3 should theoretically becircumferentially inclined the same as bailies I2. However, thesebailles also handle the downward flow in circuit c, for which baiiies I3should theoretically be circumferentially inclined in the oppositedirection. As a compromise the longitudinal axes of bailies I3 arepositioned vertically; and the variation from the theoreticallydesirable inclination is small enough to be permissible.

The form of the invention shown in Fig. 5 is generally similar inarrangement and action to the first form of the invention. The shaft 20carries a single impeller 2|, which is positioned near the bottom oftank 22. A series of baiiies 23 (three shown) are supported from thetank wall 24. These baffles are spaced from the tank wall, inclined tothe tank radius, and have their axes circumferentially inclined, all incorrespondence with baiiies I2 in Figs. 1 and 2.

The spacing of the baiiles from the tank wall eliminates pocketformations which tend to trap and localize portions of the mix.Furthermore, such spacing prevents the baffles from inter-fer ing withthe flow adjacent to the wall, where it has a tendency to be a minimum.In the forms shown in the drawing the bailles do not extend in alignmentwith the impellers, which leaves a perfectly free flow path from theimpeller to thetank wall. With liquids of low viscosity, Part of thehorizontal flow component passes between the baffles and the tank wall.This produces eddies at the restrictions, and these eddies augment theretarding eil'ect of the battles and also enhance the mixing action.

The range of viscosities to be handled determines the optimuminclinations of the battle. In determining the placement of the baflies,I prefer to do it by trial. The tank, or a substantial duplicatethereof, is filled with a transparent material of the maximum viscosityto be handled. Dark beads or other suitable objects are also placed inthe tank, so that the lines of flow can be seen. A bailie is thentemporarily inserted and adjusted into such position that it is edgewiseto the path of flow. In this way the optimum inclinations of the baille,can be predetermined for both the horizontal and vertical components offlow. In an installation which I have used for viscosities up to 60,000centipoise, the angle alpha in Fig. 3 was 55. This angle is the anglewhich the horizontal center line of the bame makes with the horizontaltank tangent intersected by the center line. The higher the maximumviscosity, the greater the baiile inclinations will be, and vice versa.

The amount of space between the baille and the tank wall which I havefound desirable is from one-half inch to one inch, per foot of tankdiameter. While the bailies may be given a curved form to correspondexactly with the flow lines at maximum viscosity, they are convenientlymade oi fiat sheet metal and with the proper placement serve adequately.The mounting of the bailles may provide for adjustment of the baffleinclinations after the installation is made, with means to lock thebaffles at the desired setting. However, it is usually simpler and moresatisfactory to predetermine the battle placement and use baiilemountings which do not provide for adjustment of the inclinations.

In compliance with the patent statutes, I have disclosed the best formsin which I have contemplated applying my invention, but the disclosureshould be considered as illustrative, not limiting.

What is claimed is:

1. In mixing apparatus of the type in which the mix is circulated by apair of vertically spaced rotating impellers mounted on a substantiallyvertical shaft, the improvement which comprises: two series of upwardlyextending bailies each adjacent to and spaced from the tank wall, thefirst series being located above the level of the upper impeller and thesecond series being located between the levels of the two impellers, thebatfies of both series having their deflecting faces inclined withrespect to the intersecting tank radii, the baifles oi the first seriesbeing also incomprises: upwardly extending bailies adjacent to andspaced from the tank wall, the baffies being located along said inclinedupward flow path and being themselves inclined upwardly andcircumferentially in the direction of impeller rotation, said baflleinclination being approximately equal to said inclination of the flowpath, and the baiiies also being inclined with respect to theintersecting tank radii and having the trailing edges of the bafflescloser to the center of the 10 tank than the leading edges of thebattles.

GORDON MACLEAN.

CERTIFICATE OF CORRECTION.

Patent No. 2,159,856.

G-ORDON HacLEAN It is hereby certified that error appears in the printedspecification of the above numbered patent requiring correction asfollows: Page 2, first column, line 6h, for the words As the flow" readAs to flow; and that the said Letters Patent should be read with thiscorrection therein that the same may conform to the record of the casein the Patent Office.

Signed and sealed this 20th day of June, A. o. 1959.

(Seal) Henry Van Arsdale Acting Commissioner of Patents.

inclined with respect to the intersecting tank radii, the baifles oi thefirst series being also incomprises: upwardly extending bailies adjacentto and spaced from the tank wall, the baffies being located along saidinclined upward flow path and being themselves inclined upwardly andcircumferentially in the direction of impeller rotation, said baflleinclination being approximately equal to said inclination of the flowpath, and the baiiies also being inclined with respect to theintersecting tank radii and having the trailing edges of the bafflescloser to the center of the 10 tank than the leading edges of thebattles.

GORDON MACLEAN.

CERTIFICATE OF CORRECTION.

Patent No. 2,159,856.

G-ORDON HacLEAN It is hereby certified that error appears in the printedspecification of the above numbered patent requiring correction asfollows: Page 2, first column, line 6h, for the words As the flow" readAs to flow; and that the said Letters Patent should be read with thiscorrection therein that the same may conform to the record of the casein the Patent Office.

Signed and sealed this 20th day of June, A. o. 1959.

(Seal) Henry Van Arsdale Acting Commissioner of Patents.

